Chondracanthus exasperatus

It is a perennial species.[7] Like many species in Gigartinaceae, the appearance of C. exasperatus can vary depending upon grown conditions.[1][3] It can be confused with Chondracanthus spinosus and Gigartina binghamiae, and it might take RFLP analysis to be sure of the species.[1][3] In addition, the names of the species in the genera Gigartina and Chondracanthus have been adjusted several times since 1961.[3] It is also similar to Mastocarpus species, known as Turkish washcloths, but is smaller, with branched blades.[8] The leaf margins of the blades are smooth in cooler water and then become toothed and jagged as the temperature increases.[3] In more exposed areas, the blades are thicker.[8] Increased water velocity will cause the blades to change shape.[9] The color of the thallus is greenish when exposed to ultraviolet light, but when it grows in deeper water it is darker red to purple.[3] Though it prefers lower water temperatures it can grow at 25 °C, but ends up dark red to black in color and having flat or cylindrical branch clusters.[10]

As originally described, C. exasperatus has a leafy stipe, with large 2–3 feet (0.61–0.91 m) long leathery-membranaceous blades that are lanceolate and simple.[11] The blade, and the majority of the thallus, is purplish-red.[7] Blade margins are thick, with rounded teeth, and appendiculate.[11] The thallus has simple, ramenta-like spiny projections (papillae) thickly strewn on both sides.[11] Coccoid pedicels are in marginal spines emerging from the thallus.[11]

C. exasperatus grows the fastest in the summer and slowest near the winter solstice.[12] Thalli have a moisture content of about 81.4% and protein content of 1.59-1.97%.[13]

C. exasperatus is found on the Pacific coast of North America from Baja California north to Sitka Sound.[7][1][14] The type locality is in Puget Sound opposite Fort Nisqually.[11] It grows on rocks in semi-exposed or semi-protected areas of the upper subtidal to lower intertidal zone,[7] down to a depth of 20m.[5]

Proliferation of invasive species such as Mazzaella japonica have a negative impact on the growth of C. exasperatus.[15] C. exasperatus is also susceptible to infection by the parasitic oomycete Pythium marinum.[16]

C. exasperatus decomposes quickly, faster than most other species, indicating its importance to detritivores and to nutrient cycling.[15] The high rate of decomposition also means that it is harder to find washed ashore as wrack and that its importance in the ecosystem may be underrepresented in research.[15]

However, amphipods such as Megalorchestia californiana and Traskorchestia spp. (including Traskorchestia traskiana[17]) will avoid C. exasperatus.[15] The isopod Ligia pallasii[17] and the green sea urchin (Strongylocentrotus droebachiensis)[15] also seems to prefer to eat other seaweed species. A diet of C. exasperatus can slow or decrease shell length in juvenile white abalone (Haliotis sorenseni) at extreme water temperatures, and possibly can be deadly at 18 °C or above raising concerns related to global warming.[13]

Commercial aquaculture in both tanks and on nets of C. exasperatus was attempted as early as the 1970s in Washington state.[18] It can also be grown in the air if sprayed with sea water, which conserves water but risks losing the crop if the pumps fail.[19] The gel within the blades has also been harvested to make cosmetics.[20] Intact blades are used in baths or for thalassotherapy, along with species such as feather boa (Egregia menziesii), finger kelp (Laminaria digitata), and Fucus.[21]